Add command line option to pass extra build args

repo2docker/__main__.py

@@ -212,6 +212,14 @@ def get_argparser():
         default=[],
     )
 
+    argparser.add_argument(
+        "--build-arg",
+        dest="build_args",
+        action="append",
+        help="Extra build arg to pass to the build process, in form name=value",
+        default=[],
+    )
+
     argparser.add_argument("--subdir", type=str, help=Repo2Docker.subdir.help)
 
     argparser.add_argument(
@@ -261,6 +269,10 @@ def make_r2d(argv=None):
         else:
             r2d.labels[l] = ""
 
+    for a in args.build_args:
+        key, _, val = a.partition("=")
+        r2d.extra_build_args[key] = val
+
     r2d.repo = args.repo
     r2d.ref = args.ref
 

repo2docker/app.py

@@ -248,6 +248,15 @@ class Repo2Docker(Application):
         config=True,
     )
 
+    extra_build_args = Dict(
+        {},
+        help="""
+        Extra build args to pass to the image build process.
+        This is pretty much only useful for custom Dockerfile based builds.
+        """,
+        config=True,
+    )
+
     json_logs = Bool(
         False,
         help="""
@@ -777,6 +786,8 @@ class Repo2Docker(Application):
                     }
                     if self.target_repo_dir:
                         build_args["REPO_DIR"] = self.target_repo_dir
+                    build_args.update(self.extra_build_args)
+
                     self.log.info(
                         "Using %s builder\n",
                         bp.__class__.__name__,